As part of this, introduce a new JSObject for iterating over the elements of a
FixedArray.

R=adamk@chromium.org,bmeurer@chromium.org
TBR=ulan@chromium.org
BUG=v8:1569

Review-Url: https://codereview.chromium.org/2407423002
Cr-Commit-Position: refs/heads/master@{#40265}